Northwest Portable Classroom Project
Retrofit Guidelines for the
Pacific Northwest
March 31, 2003
WSUCEEP03_068
Washington State University Extension Energy
Program
925 Plum Street SE
P.O. Box 43165
Olympia, WA 98504-3165
Disclaimer: These guidelines were prepared as an account of work sponsored by an agency of the United States government. Neither
the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes
any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process
disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product,
process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement,
recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed
herein do not necessarily state or reflect those of the United States government or any agency thereof.
BUILDING AMERICA EFFICIENT PORTABLE CLASSROOM PROGRAM
RETROFIT GUIDELINES FOR THE PACIFIC NORTHWEST
Purpose: To ensure the most energy-efficient operation of existing portable classrooms by providing
efficient and cost-effective envelope, air sealing and control measures. Implementation of these guidelines
will help ensure lowest life cycle costs, maintain acceptable indoor air quality and comfort standards while
providing a suitable learning environment.
These guidelines have been developed with support from the US Department of Energy’s Building
America Program partners and the Oregon Office of Energy, the Idaho Energy Division of the Department
of Water Resources and Washington State University Energy Program.
Additional information is available at: http://www.BAIHP.org
Technical assistance regarding these guidelines is available from:
•
•
•
Washington State University Energy Program - Michael McSorley: (360) 956-2008
Idaho Department of Water Resources, Energy Division – Bob Minter: (208) 327-7970
Oregon Office of Energy – Betty Merrill/Justin Klure: (503) 373–1581
Introduction: The decision to retrofit an existing portable classroom with energy-efficient measures is a
complex one. While the lack of energy-efficient envelope measures may result in costly utility bills and
comfort issues, the cost of installing most measures will likely not be cost-effective. There are specific
instances where it makes sense to retrofit:
•
•
•
In the event of a portable classroom that is scheduled for removal and demolition, retrofitting the
classroom may be extremely cost-effective, in that the cost for retrofit is much less than the cost
for disposal.
In the event that building components are replaced, they should be replaced with the most energyefficient possible.
There are specific measures that are always cost-effective, or are cost effective in most situations.
Table 1 lists the potential retrofit measures for portable classrooms, and identifies instances where
retrofitting the building component may be appropriate. Details for specific measures are listed below the
table.
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BUILDING AMERICA EFFICIENT PORTABLE CLASSROOM PROGRAM
RETROFIT GUIDELINES FOR THE PACIFIC NORTHWEST
Table 1. Recommended Portable Classroom Retrofit Specifications
Component
Description Component Nominal RRecommended
U-factor
value
Envelope Measures
Ceilings
Walls
Floors
T-Bar
Ceiling
U-0.033
R30
Rafter
U-0.033
R30
4 inch
U-0.077
R13
6 inch
U-0.053
R19
Joists
U-0.041
R30
U-0.371
Glazing
Skylights
2,3
Exterior Doors
n/a
When existing
insulation is R-11 or
less, or if insulation is
replaced
When existing
insulation is R-11 or
less, or if insulation is
replaced
If siding is removed
or insulation is
replaced
If siding is removed
or insulation is
replaced
If insulation is
replaced
If glazing is replaced
1
U-0.5
n/a
If skylight is replaced
U-0.19
n/a
If door is replaced
Air Sealing
Overall
building
leakage
Penetrations in
building
envelope
Ceiling Air
Barrier
Measured overall building leakage less
than or equal to 8 air changes per hour
(ACH) at 50 Pascals (Pa), determined by a
blower door test.
All penetrations caulked or otherwise
sealed to limit air leakage (see detail
below)
In all cases
T-bar
drop
ceiling
For all drop T-bar
ceilings
Roof
rafter
ceiling
A 4-6 mil polyethelene air
barrier shall be installed on the
warm side of the insulation and
caulked at penetrations,
overlaps and at the outside
edges of the ceiling/roof
junction.
A 4-6 mil polyethelene air
barrier shall be installed under
the insulation, stapled to the
roof rafters, and sealed with
caulk at the edges.
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As appropriate (see
detail below)
For roof rafter
ceilings, if drywall is
removed.
BUILDING AMERICA EFFICIENT PORTABLE CLASSROOM PROGRAM
RETROFIT GUIDELINES FOR THE PACIFIC NORTHWEST
Table 1. Recommended Portable Classroom Retrofit Specifications (continued)
Mechanical Systems
\HVAC control
The HVAC system shall be controlled by a
365-day programmable thermostat
equipped with an occupancy sensor for
ventilation system control.
In all cases
Ventilation
System
A mechanical ventilation system must be
provided, capable of providing 15cfm per
occupant
In all cases
Lighting
All interior ceiling lighting shall be rapid
start T-8 fluorescents with electronic
ballasts with a CRI of 75. The controls
shall be an on-off switch for each bank of
lights.
1
NFRC tested U-factor
2
Door frame shall be of thermally improved material(s).
3
Up to 1 ft2 of security glass is allowed in doors.
If fixtures are
replaced
Glazing and skylights
As the total square feet of windows is usually small in most portable classrooms (approximately 48 ft.2), it
is not cost-effective to replace old windows unless seals have failed, admitting moisture from the exterior.
Penetrations through building envelope
All penetrations shall be caulked or otherwise sealed to limit air leakage, including the following:
•
All window and door frames - sealed to the building envelope. If the seal is made on exterior
grooved siding, then the groove lines shall be sealed at the door or window frame.
•
Exterior-wall sole plates and the structural floor - caulked using silicon caulking or approved
alternate.
•
All receptacles, switches or other electric boxes in exterior walls - sealed or fitted with outlet plate
gaskets.
•
HVAC ducts - sealed at interior surfaces where ducts penetrate the building envelope.
•
Around openings in the building envelope for HVAC and ventilation ducts, and wiring.
•
All other penetrations in the building envelope.
Ceiling air barrier
Most of the portable classrooms built after 1990 do not use sheetrock ceilings; rather, they incorporate a Tbar dropped ceiling with tiles. This type of ceiling typically has no air sealing to control air leakage, and
represents a major source of heat loss in the classroom.
To combat this heat loss, a 4-6 mil polyethelene air barrier shall be installed above the ceiling tiles and
below the insulation. All penetrations through this air barrier shall be sealed with silicone caulking; the
same shall be done for any overlaps and the perimeter of the air barrier.
Portable classrooms that have the ceiling insulation installed in the roof rafters shall have the air barrier
installed under the insulation, stapled to the roof rafters, and sealed with caulk at the edges.
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BUILDING AMERICA EFFICIENT PORTABLE CLASSROOM PROGRAM
RETROFIT GUIDELINES FOR THE PACIFIC NORTHWEST
HVAC Control
Most of the portable classrooms in the Northwest region are controlled by 7 day programmable
thermostats. The result of this type of control is that the HVAC system operates throughout the year, even
during holidays and vacations. Even new units that were installed during the study exhibited this behavior.
In addition, many portable classrooms are controlled by CO2 sensors. The BAIHP study determined that
CO2 sensors can be unreliable as a control strategy, since they go out of calibration easily, and many HVAC
installers and school maintenance personnel do not have the proper equipment to calibrate them.
New low-cost, 365-day programmable thermostats are available, with occupancy sensor control for the
ventilation system; they are highly recommended for all portable classrooms, regardless of age. Estimated
simple payback for these thermostats is 2-3 years.
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